Moveable arm devices for holding a cartridge (for instance a phono cartridge) that can detect mechanical-, or may be also optical-, magnetic- or other sorts of informations, the so called tone arms, are always comprising a compromise of different point of views related to the special purpose of the tone arm in question. For instance a tone arm made of heavy materials will probably have no or just very few and small resonances, whereas tone arms made of light materials will be much more likely to have resonances, which will drastically diminish the quality of sound.
One of the most important factors for tone arms constructed for use with modern phonograph cartridges is the inertial moment of the tone arm, which must be sufficiently low to prevent the combination of cartridge and arm from oscillating and to ensure that the stylus with cantilever and the whole cartridge will always be able to accurately follow the grooves of even warped records. Such a tone arm will have to be made of very light materials, which are usually causing many resonances.
The purpose of the invention is to obtain a tone arm having no or just few resonances and having a very low inertial moment as to the point around which the arm is moving and on which--if desired--it is also possible to change out a minor part of the tone arm--the arm tube or -rod--carrying the cartridge in order to make it easy to change to another cartridge. Another purpose is that the point around which the vertical movement of the arm takes place should be positioned close to the horizontal plane in which the surface of the record is positioned, and further it is a purpose of the invention to make an adequate skating force compensation.